1. Technical Field
This invention relates to semiconductor device manufacturing, and more particularly to the post chemical mechanical polishing (CMP) cleaning of semiconductor substrates.
2. Background Information
During the manufacture of semiconductor devices, after particular manufacturing steps, it is desired or required to remove contaminant particles. If not removed, such particles may cause defects in the device being manufactured or otherwise interfere with the manufacturing process.
For example, integrated circuits are typically formed on silicon wafers by the sequential deposition of conductive, semiconductive or insulative layers. After each layer is deposited, the layer is etched to create circuitry features. After a series of layers are sequentially deposited and etched, the outer or uppermost surface of the substrate, i.e., the exposed surface of the substrate, becomes increasingly nonplanar. The substrate may be periodically planarized via a process such a chemical mechanical polishing. This method typically includes the mounting of the substrate on a carrier or polishing head and the placing of the exposed surface of the substrate against a rotating polishing pad. A polishing slurry, which may include chemically-reactive agents and/or abrasive particles, may be introduced to facilitate the polishing. The polishing leaves the surfaces of the substrate contaminated with polishing byproducts typically including silica, alumina, or other abusive particles from the slurry as well as a variety of other particles. Other residues from the polishing include the slurry itself, and often rubber or lubricant residue left by the carrier on the unpolished surface of the substrate.
A variety of methods and apparatus have been used or proposed for substrate cleaning after CMP. Broadly characterized, these include immersive and spray techniques. One immersive technique involves placing the substrates in an alkaline solution of ammonium hydroxide, water and hydrogen peroxide, and subjecting the solution to ultrasonic agitation to remove contaminants. The substrates may then be rinsed and dried.
Prominent among spray techniques are a variety of cryogenic techniques. Such techniques require the use of a high pressure gas and frequently may include the introduction of a cleaning agent. The cleaning agent is frozen by the expansion of the gas through a nozzle and is thus impinged upon the surface of the substrate as a spray of frozen particles. Cryogenic methods typically make intensive use of the gas which may prove expensive.
Somewhat intermediate of the immersion and spray methods are methods which involve directing a stream of liquid onto a substrate surface being cleaned. A liquid cleaning agent is sprayed from a high pressure nozzle, with an associated high kinetic energy, for dislodging small particles from the surface. Such methods may make intensive use of the cleaning agent, with a relatively large droplet or jet size as compared with the size of the particles being removed. Thus, in addition to the high cost of the high volume of cleaning agent, expensive high pressure pumps may be required and the cleaning agent may need to be filtered to avoid damage to the substrate. Accordingly, it is desirable to provide a substrate cleaning system and method which is efficient in its use of consumable products such as cleaning agent and does not present high equipment costs.